This relates generally to wireless communications circuitry, and more particularly, to circuitry in wireless electronic devices that reduces interference from frequency harmonics and simultaneously receives radio-frequency transmissions in different frequency bands.
Electronic devices such as computers and cellular telephones are often provided with wireless communications capabilities. For example, electronic devices may use long-range wireless communications circuitry such as cellular telephone circuitry. Global Positioning System (GPS) receiver circuitry and other satellite receiver circuitry may be used to receive satellite navigation signals. Local wireless links may be used to support local area network communications such as IEEE 802.11 communications at 2.4 GHz and 5 GHz. Local links may also be used to handle Bluetooth® communications at 2.4 GHz.
It is often desirable for a device to support multiple bands. For example, users of a cellular telephone may desire to communicate with cellular telephone towers using one or more different cellular telephone bands and may desire to communicate with local area network equipment using wireless local area network (WLAN) communications bands.
When supporting multiple bands, it is sometimes desirable to use configurable switching circuitry to route signals. In a device having a transceiver with numerous transceiver ports, for example, a switch may be used to selectively couple a selected one of the transceiver ports to an antenna. This type of configuration allows the device to be configured in different ways, depending on the desired band of operation. If, for example, it is desired to use a first communications band, the switch may be placed in a first state that couples a first transceiver port to the antenna. When it is desired to use a second communications band, the switch may be placed in a second state that couples a second transceiver port to the antenna.
Radio-frequency switches may be based on components such as transistors that exhibit non-linear behavior. As a result, undesired frequency harmonics may be generated when radio-frequency signals are transmitted through a switch. For example, second harmonics, third harmonics, and higher-order harmonics of transmitted radio-frequency signals may be generated. If care is not taken, these harmonic signals may interfere with the operation of receiver circuitry in the device. For example, harmonics that are generated during transmission of cellular telephone signals may interfere with proper operation of a satellite navigation receiver or wireless local area network receiver.
Wireless devices may be required to simultaneously receive radio-frequency transmissions in two or more frequency bands. For example, a wireless cellular device that communicates with a base station using a Long Term Evolution (LTE) protocol may be required to receive radio-frequency transmissions from the base station in two separate LTE bands.
To handle wireless communications in environments such as these, it would be desirable to be able provide improved circuitry for routing signals between radio-frequency transceiver ports and antenna structures in a wireless electronic device.